The present invention relates to a regenerative pump for pressurizing and supplying a fluid, and a casing thereof, which pump is suitably used as a fuel pump for an automobile.
Generally, a regenerative pump is used as a small-sized pump which delivers a small amount of liquid of a low viscosity under a high pumping pressure, and it has recently been employed as, for example, a fuel pump for an automobile. In the case of such a fuel pump, to satisfy present social demands such as saving of natural resources and environmental protection, reduction of fuel consumption (decrease of the alternator load) by improving the pumping efficiency has been an important technical problem in recent years.
By the way, in a regenerative pump of this type, a fluid pressurized and supplied by an impeller is delivered to a discharge port after it collides against a terminal end portion of a pump flow passage. At this time, the fluid on the casing body side, i.e., on the side where the discharge port is formed, can move to the discharge port. However, the fluid on the casing cover side, i.e., on the side where no discharge port is provided, stops against the inner peripheral portion of the flow passage, conspicuously increasing a pressure of the fluid. Besides, when the circumferential direction of the impeller is considered, the pressure of the fluid in the vicinity of the front side of vane members (the downstream side of the fluid flow) is the highest so that the pressure will be increased periodically every time the vane members are located at the terminal end portion of the flow passage during the rotation, thereby generating noises of a frequency corresponding to a product of the number of the vane members and the rotational speed.
The following has been known as a technique for preventing such noises at the terminal end portion of the flow passage.
A water pump which utilizes a regenerative pump (Westco pump) is disclosed in Japanese Utility Model Unexamined Publication No. 56-120389. In this pump, as shown in FIG. 22, an inclined surface 23 is formed at a terminal end portion of a fluid passage 22 which is formed in a casing cover 21. Consequently, a fluid which has been pressurized and supplied through the fluid passage 22 by the rotation of an impeller 24 successively collides against the inclined surface 23 so that noises caused by collision of the fluid can be reduced as compared with the structure in which the terminal end portion is closed by a vertical wall.
A fuel pump which utilizes a regenerative pump is disclosed in Japanese Utility Model Unexamined Publication No. 2-103194. This fuel pump comprises an impeller including vane grooves formed in peripheral edge portions of both the surfaces of the impeller, and a casing in which this impeller is housed. In this conventional technique, noise reduction has been tried. A chamfered surface 27, as shown in FIG. 24, is formed in a terminal end portion of a fluid flow passage 26 of a casing cover 25, as shown in FIG. 23. As a result, noises at the terminal end of the flow passage can be reduced.
However, the above-described structures of the conventional techniques involve a problem that sufficient noise reduction can not be effected.
This problem is induced for the following reasons. For example, in the pump shown in FIG. 22, since the terminal end of the inclined surface 23 is closed on a straight line in parallel to each vane of the impeller, the fluid which has collided against the inclined surface 23 eventually collides on the boundary line at the terminal end of the inclined surface 23 at once, so that noises can not be sufficiently reduced. Further, even if the terminal end of the flow passage is circular, as shown in FIG. 23, the fuel collides against the circular terminal end surface at once without much time differences, and therefore, noises can not be sufficiently reduced. Moreover, in the configuration shown in FIG. 22 or 23, substantially the entire surface of each vane of the impeller enters a partition portion simultaneously, so that noise reduction can not be adequately effected.
Furthermore, the inclined surface and the chamfered surface described above involve a problem that it is difficult to work the pump flow passage into a desired shape while maintaining the plane accuracy of the inner surface of the casing.
The inner surfaces of a casing body and a casing cover require a high plane accuracy because the impeller slidingly moves therein. Therefore, the inner surfaces of the casing body and the casing cover formed by die casting are ground to obtain a predetermined plane accuracy. In this case, when an inclined surface or a chamfered surface is formed on the casing cover or the casing body, as in the conventional techniques, the terminal end line of the inclined surface or the terminal end line of the chamfered surface is deviated as a result of grinding of the inner surface.
If inclined surfaces or chamfered surfaces are formed on both the casing cover and the casing body, the inner surfaces of the casing body and the casing cover are ground individually so that the terminal end line on the casing cover side may be deviated from the terminal end line on the casing body side in every product, as indicated by the dashed line in FIG. 24. Such a deviation of the terminal end lines causes a variation in the length of a sealed portion formed between the discharge port and the suction port, which results in a fear that a constant performance can not be obtained.
In this manner, the conventional techniques have not only the problem that sufficient noise reduction can not be effected but also the problem that the configurations are not suitable for practical use.